1. Field of the Invention
The present invention relates to an angular velocity detection circuit in a vibrating gyroscope, for example, an angular velocity detection circuit in a vibrating gyroscope for detecting an angular velocity based on an oscillation output of a vibrating gyroscope including a bimorph vibrator for use in correction of camera-shake, a navigation system, and so forth, and to a method of detecting angular velocity.
2. Description of the Related Art
FIG. 11 is a schematic perspective view showing an example of a conventional bimorph vibrator for use in a vibrating gyroscope. In FIG. 11, the bimorph vibrator 1 is formed by two piezoelectric element sheets having polarization directions which are opposite to each other (as shown by the oppositely facing arrows), and which are bonded to each such that the vibrator 1 has a rectangular cross-section. When the vibrator 1 vibrates in the longitudinal mode, i.e., vibrates in the X-axis direction, and the vibrator is rotated at an angle (xcexa9) about the Z-axis direction, vibration is generated in the transverse vibrating mode, i.e., in the vertical Y-axis direction, due to the Coriolis force.
The amplitude of this vibration is proportional to the angular velocity. Thus, the angular velocity can be detected by utilizing the proportional relation. The vibrator 1 is provided with right and left electrodes 1R and 1L, respectively, and a common electrode (not shown). A differential output signal of a left signal and a right signal is output from the right and left electrodes 1L and 1R, respectively. For the above described vibrator 1, it is necessary to adjust the balance, the null voltage (also called an offset voltage or a neutral point voltage), the sensitivity, and so forth, individually.
FIG. 12 is a block diagram of an angular velocity detection circuit for producing an output from the vibrator 1 shown in FIG. 11. In FIG. 12, the differential output signal from the vibrator 1 is amplified in a differential amplification circuit 21. The amplified waveform is detected in a synchronous detection circuit 22 and smoothed in a smoothing circuit 23. The produced DC voltage is DC amplified in a DC amplifier 24. When the signal is amplified in the DC amplifier 24, the null voltage is also DC amplified. Accordingly, the DC component is cut off in a DC cut circuit 25 comprising, e.g., a filter. The signal is further amplified in an amplification circuit 26 to be output as an analog signal. Then, the analog signal is converted to a digital signal in an A/D converter 27. Thereafter, the angular velocity detection signal is supplied to a microcomputer 28, so that camera-vibrating shake is suppressed, or control for navigation is carried out.
Generally, a conventional gyroscope chip includes the vibrator 1 through the amplifier 26. As a result, the conventional vibrating gyroscope chip tends to become large in size. In addition, it is necessary for an apparatus installed with a vibrating gyroscope to employ an A/D converter. There is a great demand for a vibrating gyroscope which can output a digital signal corresponding to a detected angular velocity, thereby enabling cost reduction of the vibrating gyroscope, as well as cost reduction of the entire the apparatus installed within the vibrating gyroscope.
The conventional gyroscopes have additional drawbacks. Specifically, when a signal component is amplified in the DC amplifier 24 in the angular velocity detection circuit shown in FIG. 12, the null voltage is also amplified. If the gain of the DC amplifier is high, the fluctuation of the null voltage in response to the change in temperature become so large to affect the detection of a signal representing the angular velocity. For this reason, the gain of the DC amplifier 24 cannot too large.
Furthermore, the null voltage cannot become 0V due to the unbalance between the right signal and the left signal. As a result, the gain of the DC amplifier 24 has to be so small that the null voltage does not saturate at power voltage or the ground potential, regardless of the fluctuation of the null voltage.
In addition, if a high pass filter for passing a signal having a frequency of at least 0.1 Hz is formed to cut the DC component in the DC cut circuit 25, it is necessary to provide a combination of a 20 xcexcF large capacitance capacitor and a 1 Mxcexa9 resistor for the high pass filter. Thus, a large-sized apparatus is required.
Furthermore, in the circuit shown in FIG. 12, the output signal is output from the differential amplification circuit 21 with the right and left signal components being out of phase in some cases, and with the amplitudes of the right and left signal components being shifted, in other cases. In the case in which the amplitudes are shifted from each other, the amplitude of the differential output is simply changed, since the right and left signal components are sine waves. On the other hand, when the right and left signal components are out of phase, the output signal is out of phase with the reference signal.
As another conventional example, Japanese Examined Patent Application Publication No. 6-13970 describes that a drive signal is applied to the detection sideface of a vibrator in such a manner that the phase difference angle between the vector of an output voltage, caused by the angular velocity when a vibrator is rotated, and the vector of the null voltage when the vibrator stops, becomes 90xc2x0. The angular velocity is detected based on a phase difference in the combined vector.
In this example, the amplitude of the output from the vibrator has a linearity. On the other hand, the relation between the phase difference and the sensitivity is not linear, and the non-linearity tends to change in accordance with the null phase. For this reason, it is desirable to digitize the amplitude of the Coriolis force.
For example, Japanese Unexamined Patent Application Publication No. 62-150116 describes that sample-and-hold is carried out at the time when the angular velocity, caused by oscillation-driving, becomes maximum and minimum.
Furthermore, in Japanese Unexamined Patent Application Publication No. 7-260493, it is described that a difference in current passing through a piezoelectric device is detected, and sample-hold is carried out at the timing when the displacement velocity of a vibrator detecting the difference becomes zero. However, it is not described how the sample-and-held signal is digitized.
Japanese Unexamined Patent Application Publication No. 8-146056 discloses a phase difference detection circuit for a gyroscope. Although the circuit outputs signals which can be directly processed by a microcomputer, the phase difference of the detected signal is adversely affected by the change of the temperature. That is, the phase difference detection circuit has a problem that it is difficult to detect an angular velocity precisely and stably.
Accordingly, it is a main object of the present invention to provide an angular velocity detection circuit for a vibrating gyroscope which can output a digital signal corresponding to a detected angular velocity. Another object of the present invention is to provide an angular velocity detection circuit for a vibrating gyroscope in which a null voltage can be detected and corrected.
The present invention also provides a vibrating gyroscope comprising such an angular velocity detection circuit and a method of detecting an angular velocity.
In accordance with a first aspect of the invention, a method of detecting angular velocity comprises generating a differential signal from a vibrator, the differential signal having a Coriolis force proportional to angular velocity if the vibrator is rotated; generating a timing signal based on the differential signal; and applying the differential signal to a voltage-time converter which, based on the timing signal, converts the differential signal to a pulse train having a duty cycle proportional to the angular velocity.
In accordance with another aspect, the invention is directed to an angular velocity detector, which comprises a vibrator for generating a differential signal, the differential signal having a Coriolis force proportional to angular velocity if the vibrator is rotated and having a null value; a differential circuit for detecting the differential signal; a timing circuit for generating a timing signal based on the differential signal detected by the differential circuit; and a voltage-time converter for receiving the differential signal detected by the differential signal detected by the differential circuit which, based on the timing signal, converts the differential signal to a pulse train having a duty cycle proportional to the angular velocity.
According to still another aspect of the present invention, the differential signal is derived from first and second outputs of the vibrator and the angular velocity is detected by generating a reference signal from a sum of the first and second output signals, generating a timing signal based on the reference signal and sample-and-holding the differential signal based on a timing signal to generate a sample-hold signal. The differential signal includes a component due to Coriolis force. The sample-hold signal is then integrated and compared with a predetermined level to generate a digital signal having a duty cycle proportional to the angular velocity. The angular velocity is then determined based on the duty cycle.
The invention, according to a further aspect, provides an angular velocity detector, which comprises a vibrator for generating a differential signal from first and second outputs of the vibrator, the differential signal having a Coriolis force proportional to angular velocity if the vibrator is rotated and having a null value; a differential circuit for detecting the differential signal; a reference signal generator for generating a reference signal from the sum of the first and second outputs of the vibrator; a timer for generating a timing signal based on the reference signal; a sample-and-hold circuit for sampling-and-holding the differential signal detected by the differential circuit based on the timing signal to generate a sample-and-hold signal; an integrator for integrating the sample-and-hold signal; a comparator for comparing the integrated sample-and-hold signal with a predetermined level to generate a digital signal having a duty cycle proportional to the angular velocity; and means for determining the angular velocity from the duty cycle of the digital signal.
According to still another aspect of the invention, the predetermined level is such that when there is no Coriolis force the duty cycle is zero.
According to still another aspect, the invention provides an angular velocity detection circuit, which comprises a differential circuit for generating a differential signal, the differential signal having a Coriolis force proportional to angular velocity; a timing circuit for generating a timing signal based on the differential signal detected by the differential circuit; and a voltage-time converter for receiving the differential signal detected by the differential signal detected by the differential circuit and which, based on the timing signal, converts the differential signal to a pulse train having a duty cycle proportional to the angular velocity.
According to a further aspect, the invention provides an angular velocity detecting circuit, which comprises a differential circuit for generating a differential signal from first and second input signals, the differential signal having a Coriolis force proportional to angular velocity and having a null value; a reference signal generator for generating a reference signal from the first and second input signals; a timer for generating a timing signal based on the reference signal; a sample-and-hold circuit for sampling-and-holding the differential signal detected by the differential circuit at times based on the timing signal to generate a sample-and-hold signal; an integrator for integrating the sample-and-hold signal; a comparator for comparing the integrated sample-and-hold signal with a predetermined level to generate a digital signal having a duty cycle proportional to the angular velocity; and means for determining the angular velocity from the duty cycle of the digital signal.
In accordance with yet another aspect of the present invention, the time range of integration is extended to increase resolution level.
According to the invention, duplicated circuits for digitizing synchronous detection or the like, employed conventionally, can be eliminated. Thus, cost-saving can be realized.
Moreover, the circuit configuration of the V-T conversion means can be simplified preferably by using a sample-and-hold circuit which provides a linear decreasing output over time.
Furthermore, control can be carried out so that the null voltage is zero at any time, and effects of changes in temperature on the null voltage can be canceled preferably by comparing the sample-and-hold values at a particular phase point in a first sampling period and at a phase point different from the above phase point in another sampling period to estimate the null differential voltage, and controlling the level of the comparison means, based on the estimated null differential voltage.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.